For relatively heavy vehicles such as locomotives, tractors, or automobiles a continuously variable transmission ratio is required because of the wide range of operating conditions. For example, in accelerating a locomotive from a standstill, a very high output torque is required even though the horsepower is low. As the locomotive gains speed, it is desirable to deliver maximum horsepower from the engine from its low to a maximum speed in order to achieve the shortest possible acceleration cycle. Once the locomotive is at cruising speed, it becomes desirable to operate the engine at a rotative speed that will result in the minimum specific fuel consumption for the needed power output. Thus, heretofore the objective of mechanical torque converter development has been to provide a transmission that will transfer power from a prime mover to a load with a controllable speed ratio.
Torque converters cause a working mass to undergo an acceleration/deceleration cycle wherein the accelerative forces are provided by the prime mover and a reaction member(s), and the deceleration forces are provided by the output member. The impulses caused by these accelerations/decelerations cause the prime mover to do work on the output member. A stationary reaction member is required to exert forces on the mass without contributing work if a torque multiplication is to occur. The most common type of torque converter is the hydrodynamic type, wherein the working mass is a fluid, the accelerating means is a turbine/pump, the output means is a turbine, and the reaction member is a set of fixed vanes. The losses in a hydrodynamic converter are substantial because of turbulence and viscous friction, and the torque conversion (increase) is typically less than 3.
The prior art utilized either selectable sets of gears with particular ratios, sometimes supplemented with hydrodynamic torque converters that extended the ratio range and allowed shifting of gear sets without shock. Other systems included motor/generator sets driven by the prime mover, or variable displacement hydraulic pump/motor sets driven by the prime mover. All of these devices involved either functional compromises, noise or durability problems, and all operated with significant losses. Smaller transmissions sometimes used variable pitch Vee belt drives, variable pitch diameter traction (friction) drives, or incrementing drives with variable stroke such as using over-running mechanical clutches. These transmissions typically exhibited poor durability. A general object of the present invention is to overcome these problems with a mechanical torque converter wherein all moving masses and members are supported by antifriction bearings, with only relatively insignificant electromagnetic, electrical, and windage losses so that high torque conversion ratios with high efficiency are provided within a wide speed range.
Another object of the invention is to provide a mechanical torque converter with controllability features that include: inherent output torque control by controlling the relative speed of the input with respect to the output speed; and control of the rate of torque increase with increase of differential speed.
Another object of the invention is to provide a mechanical torque converter with a wide operating range which is applicable to various power transmission systems.
Still other objects of the invention are to provide a mechanical torque converter: that has high input to output efficiency throughout its operating range; that is highly controllable with respect to input and output speed and torque; and is highly durable since it has a minimum of wearing or sliding parts and has a high degree of immunity from any shock due to abrupt changes in output load.